1. Field of the Invention
This invention relates generally to gas lift valves for the artificial production from oil and gas wells and, more particularly, to gas lift valves capable of operating at high differential pressures.
2. Description of Related Art
Gas lift valves have been used for many years to inject compressed gas into oil and gas wells to assist in the production of well fluids to the surface. The valves have evolved into devices in which a metal bellows, of a variety of sizes, converts pressure into movement. This allows the injected compressed gas to act upon the bellows to open the valve, and pass through a control mechanism into the fluid fed in from the well's producing zone into the well bore. As differential pressure is reduced on the bellows, the valve can close. Two types of gas lift valves use bellows. The first uses a non-gas charged, atmospheric bellows and requires a spring to close the valve mechanism. The other mechanism uses an internal gas charge, usually nitrogen, in the bellows and volume dome to provide the closing force for the valve. In both valve configurations, pressure differential on the bellows from the injected high pressure gas opens the valve mechanism.
In the case of the non-gas charged bellows, the atmospheric pressurized bellows is subjected to high differential pressures when the valve is installed in a well and exposed to high operating gas injection pressure. The nitrogen charged bellows is subject to high internal bellows pressure during setting and prior to installation. Once installed, the differential pressure across the bellows is less than in a non-gas charged bellows during operation of the valve. High differential pressure across a bellows during operation reduces the cycle life of the bellows. The existing gas lift valves and bellows are not designed to operate with set pressures or in operating pressures in excess of 2000 psig without severe failure risks. Some existing valve bellows do have some fluid and/or mechanical protection for overpressure due to operating pressures in the fill open position. However, none provide for protection from differential overpressure from the set pressure in the bellows.